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Kim et al. Soft Sci 2023;3:16 https://dx.doi.org/10.20517/ss.2023.07 Page 21 of 30

electronics, optoelectronics, energy devices, biomedical devices, sensors, actuators, and metamaterials to
microfluidic systems. Although each of the technologies discussed in this article has unique functionality
and outstanding performance, there are still areas that can be improved.

First, maintaining the unique functions via 3D geometry depends on structural stability against external
stimuli, such as temperature changes, rain, and vibration. Understandably, there are a number of related
challenges. Materials that use light to trigger the reconfiguration of 3D structures generally exhibit low
thermal stability, so the discovery of active materials that respond only to single stimuli is expected to play
an important role in improved mechanical stability. In addition, 3D structures consisting of ultra-thin film
scaffolds may have difficulty maintaining their structure in harsh environments. The mechanical stability
may be improved by introducing a support layer through methods such as initiated chemical vapor
deposition (iCVD). 3D structures made of non-stretchable materials that are affected by vibration or wind
will require a high level of energy dispersion in their structural design to resist external forces. There are
also several improvements required in terms of applicability. For example, chip-level applications via 3D
assembly at the nanoscale have been realized, but devices with high chip integration density have rarely
been reported. In addition, the resulting yield and success rate of 3D structure fabrication must be further
improved to meet the requirements of device mass production.

In this respect, further advances in 3D structure manufacturing technologies will pave the way for the
development of devices with novel functions and improved performance. For 3D printing technologies that
provide a high level of geometry control, it will be necessary to expand accessibility to high-performance
materials and increase processing speed. Origami and kirigami methods, which operate at high speed under
systematic rules, require new schemes to avoid manual intervention that hinders the realization of structural
complexity and functionality at the micro and nanoscale. Finally, design capabilities for mapping 3D
structures to 2D precursors in mechanically-guided assemblies are in the early stages of development, and
design rules for more complex geometries are required. As a result, the application fields for 3D structures
with flexibility and stretchability are also expected to expand as the manufacturing technology of 3D
structures develops. For example, electronics embedded with 3D structures will create a variety of design
opportunities that are lacking in 2D electronics within electrical engineering. In addition, the development
of 3D multifunctional devices in the biomedical field will provide opportunities for research and clinical
medical device development. These devices will also serve as a growth platform for the development of new
research tools enabling material science exploration and discovery. Therefore, developing flexible/
stretchable 3D structures will allow for novel research in many fields of study and will lead to
unprecedented engineering applications.

The impressive advances outlined in this review will provide a strong incentive for research related to
applications that can benefit from or are activated by 3D geometry. Furthermore, the question of how 3D
structures can be utilized will shift to how they can be integrated further with various engineering fields,
including electrical engineering, mechanical engineering, chemical engineering, cell biology, and biomedical
engineering, to open new application areas.

DECLARATIONS
Authors’ contributions
Supervised the overall direction and edited the manuscript: Kim BH
Configured the figure set and wrote the manuscript: Kim JH, Lee SE